The present invention relates generally to opening arrangements for packing containers. More specifically, the present invention relates to an opening arrangement for a packing container made of a multi-layer or laminated material and including a material strip applied over a pouring opening of the container which strip is sealed in a liquid-tight manner to the container material.
In non-returnable packages for pressurized contents, e.g. beer or carbonated beverages, the internal pressure in the package makes it difficult to design the package in such a manner that it is of sufficient strength and tightness, especially after prolonged storage in a warm environment. Special strength problems arise in the opening arrangement of the packing container, since it must present good strength and tightness while being openable without excessive effort. The opening arrangement frequently consists of a hole or a pouring opening punched out in the flexible packing material which is covered by a likewise flexible plastic strip which by heat-sealing forms a liquid-tight joint with the packing container material around the pouring opening (so-called pull-tab). The seal between the strip and the packing container material is achieved by fusing together the materials, which provides satisfactory strength and tightness, but as a result also renders appreciably more difficult the removal of the strip, so that the packing container cannot readily be opened.
Packing containers of the abovementioned type can be manufactured at present from flexible plastic laminate which comprises a number of layers of plastic material of different properties joined to one another. A typical material suitable for pressurized packing containers may consist e.g. of three layers of polyester joined together, the central polyester layer being biaxially oriented, so as to give the laminate good mechanical strength and low extensibility while the two outer layers are amorphous to allow sealing together of the packing container with the help of heat.
It is an object of the present invention to provide a packing container of this type with an opening arrangement which, by a good margin, resists the internal pressure in the packing container and which presents good tightness against liquid as well as gas. These and other objects have been achieved in accordance with the invention in that an opening arrangement of the type described in the introduction has been given the characteristic that the mutual bond between the material layers included in the container material is weaker than the seal between the strip and the container material. Owing to the aforementioned adaptation of the strength of seal between the strip and the packing laminate in relation to the strength of seal between the material layers included in the packing laminate it is possible to provide a strong bond between the strip and the packing laminate, so that the weld stands up well against the stresses caused by the internal pressure. These stresses make themselves felt largely as tensile stresses directed in the plane of the laminate (and of the strip). At the same time as the strong bond is provided, the forces occurring on opening of the packing container (largely directed at an angle of 90.degree. to the plane of the packing container laminate) achieve relatively easily a delamination between the layers of the packing laminate so that not only the strip, but also a part of the outer, weaker layer of the laminate is entrained.
On opening of the packing container, cracks readily appear in the edge of the pouring opening at the moment when the tearing is initiated and the material starts to break, since the pouring edge at this moment is subjected to the combined effect of the tensile force in the strip and the pressure effect from the contents. In accordance with a preferred embodiment of the invention it has been possible to avoid these cracks by having the seal between the strip and the packing laminate extend around the pouring opening at a little distance outside this edge line. By virtue of this design the edge itself will be permanently in an unstressed and non-loaded condition, so that the cause of crack formation is effectively eliminated.
It is a further object of the present invention to provide a pouring edge formed in the packing laminate which is not deformed through stresses on storage or opening of the packing container and which does not disturb the tightness or the function of the opening arrangement.
These objects have been achieved in accordance with the invention, in that the pouring opening along a part of its periphery has a pouring edge which delimits a countersunk area situated close to the pouring opening. The pouring edge is thus situated wholly inside the plane which is defined by the outside of the laminate, so that it does not disturb the close contact of the strip against the outside of the laminate or in some other manner renders difficult the application or removal of the strip. Moreover, since the pouring edge is situated in the non-sealed area around the actual pouring opening, it is also not subjected to any one-sided pressure from the contents, so that it does not have to be dimensioned so as to permit any appreciable stress.
Further embodiments of the opening arrangement in accordance with the invention have been given the characteristics which are evident from the description below.